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Indirectly, the expression of particular genes may be assessed with DNA microarray technology, which can provide a rough measure of the cellular concentration of different messenger RNAs; often thousands at a time. While the name of this type of assessment is actually a misnomer, it is often referred to as expression profiling. The expression of many genes is known to be regulated after transcription, so an increase in mRNA concentration need not always increase expression. A more sensitive and more accurate method of relative gene expression measurement is real-time polymerase chain reaction. With carefully constructed standard curve it can even produce an absolute measurement such as in number of copies of mRNA per nanolitre of homogenized tissue, or in number of copies of mRNA per total poly-adenosine RNA. Protein expression levels can be measured by fusing the desired protein to another reporter protein, such as the green fluorescent protein or the enzyme beta-galactosidase. The expression level of these reporter proteins can be directly quantitated using standard techniques.

Genes have sometimes been regarded as nodes in a network, with inputs being proteins such as transcription factors, and outputs being the level of gene expression. The node itself performs a function, and the operation of these functions have been interpreted as performing a kind of information processing within cell and determine cellular behaviour.